Cation-π interactions enabled water-stable perovskite X-ray flat mini-panel imager

Sensitive and stable perovskite X-ray detectors are attractive in low-dosage medical examinations. The high sensitivity, tunable chemical compositions, electronic dimensions, and low-cost raw materials make perovskites promising next-generation semiconductors. However, their ionic nature brings serious concerns about their chemical and water stability, limiting their applications in well-established technologies like crystal polishing, micro-processing, photolithography, etc. Herein we report a one-dimensional tryptamine lead iodide perovskite, which is stable in water for several months as the strong cation-π interactions between organic cations. The one-dimensional and two-dimensional tryptamine lead iodide perovskite tablets are switchable through thermal-annealing or water-soaking treatments to relax microstrains. The water-stable and microstrain-free one-dimensional perovskite tablets yield a large sensitivity of 2.5 × 106 μC Gyair−1 cm−2 with the lowest detectable dose rate of 5 nGyair s−1. Microelectrode arrays are realized by surface photolithography to construct high-performance X-ray flat mini-panels with good X-ray imaging capability, and a record spatial resolution of 17.2 lp mm−1 is demonstrated.

In the unit cell of the 1D perovskite (Supplementary Figure 2a), three octahedrons are connected in turn by face contact and edge contact, forming the repeat unit of the inorganic part, and between these two columns of the inorganic octahedron, four TA molecules are divided into two parallel groups, with each group of the parallel molecules arranged in reverse order.Williamson-Hall (W-H) calculation and fittings for the tablets with various heating times are shown in Supplementary Figure 4. Microstrain (ε) is obtained from the slope of the fitted line.As plotted in Supplementary Figure 3d, the microstrain decreased by magnitude (0.1875 to 0.020) after several hours of thermal annealing, demonstrating the microstrain relaxation process induced by thermal annealing.We found that the T-2D tablet can switch back to the T-1D/F-1D tablet upon water soaking or moisture treatment.To provide a wild transition process from 2D to 1D, we built an environment with high humidity for the dimension transition from 2D to 1D.As shown in Supplementary Figure 6, a glass culture dish filled with water was placed on a hot plate and then covered the dish with a beaker.When we raise the temperature of the hot plate, moisture will fill in the limited area, thus resulting in a high-humidity environment.Based on the previous XRD characterization and W-H calculation results during the tableting and transition processes.When the perovskite powder was tableted as the tablet, an enlarged microstrain in the perovskite lattice was induced.We showed this microstrain generation process as schemed in Supplementary Figure 8.As shown in Supplementary Figure 10a, three kinds of interactions exist in the 1D perovskite (TA4Pb3I10), including halogen bonding between the Pb-I octahedrons and TA cations, - interactions between indole rings and cation- interactions between pyrrole rings and the ethylamino of the neighboring TA + , Supplementary Figures 10b and 10c exhibit the strong cation- and - interactions between the closely packed TA ions, separately.And Supplementary Figure 10d shows the halogen bonding in 1D perovskite.In contrast, only halogen bonding and relatively loose - interactions exist in the optimized 2D structure (TA2PbI4) (Supplementary Figure 10e), which means a relatively loose arrangement in the 2D structure.Supplementary Figure 12: IR measurements of the reversible dimension transition process.
Liquid NMR measurements were performed to confirm the structure of the TAI molecule.
Based on the results, the pyrrole nitrogen is unprotonated.As depicted in Supplementary Figure 13, TAI and TAI-PbI2 in deuterated DMSO have an utterly consistent chemical shift, indicating the entirely consistent chemical environment of hydrogens, proving that TAI molecules present a monodispersed state, whether with or without PbI2.On the contrary, when we take the deuterated acetonitrile as the solvent to perform the same experiments, the chemical shift of the TAI-PbI2 sample shifted compared with pure TAI molecules (Figure 3b), demonstrating that intermolecular interactions occurring in the precursor solution of TAI-PbI2 in ACN.The indentation curves of the tablets are shown in Supplementary Figure 16, and we can see that all the indentation depths of MAPbI3, PEA2PbI4, and Cs2AgBiBr6 perovskites are deeper than 3000 nm.In contrast, TA-based perovskite tablets show shallower than 3000 nm with more robust resistance to plastic deformation.
The F-1D tablets were obtained after various water-soaking times, and then we dried the tablets on a hot plate at the temperature of 120℃ for ~3 hours.After this, the dried tablets were fabricated into the device with the structure of Au/perovskite tablet/C60/BCP/Cr as the active layers.
The corresponding response sensitivity to hard X-ray with a tube voltage of 120 kVp is plotted in Figure 4b, and the sensitivity fitting lines are shown in Supplementary Figure 17.In order to explore the long-term soaking stability of the tablet material in water, we soaked a tablet with 2D structure in water for 48 days.After soaking for only 1 minute, the 2D tablet started to transfer to the 1D structure and kept the 1D structure for the next 48 days.NED characterization.To confirm the minimization dose to the medical imaging patient, we performed NED value of the F-1D flat panel detector based on the reported noise experiments method 4 , the resulted NED of 118 nGy is comparable to the reported scintillators 5 .
Supplementary Figure 19: NED of the F-1D flat panel detector.The integration time is 300 ms.
The sensitivity of A-1D (Supplementary Figure 20a) and F-1D tablets (Supplementary Figure 20b) to the hard X-ray of 120 kVp was characterized under different operating temperatures.
Comparing the two figures, we can see the larger response current in the F-1D case than in the A- Based on the on-off raw data shown in Supplementary Figure 20, we obtained the signal current by subtracting the adjacent dark current (off) from the radiated current (on) and plotted the signal current under different radiation dose rates in Supplementary Figure 21.Then the signal plots were fitted in a line, and the slope represented the sensitivity of the tablet material.The corresponding sensitivities under different temperatures were plotted in Figure 4d, which showed  the increased tendency of sensitivity with increasing temperature in the F-1D case.In contrast, a decreased tendency occurred in the A-1D case.μτ product, which determines the charge collection capability and device signal intensity, is an essential parameter for an X-ray detector.We derived the μτ product by fitting the X-ray photoconductivity curves to the modified Hecht equation 6,7 .The corresponding fitting curves are shown in Supplementary Figure 22.The A-1D tablet had a μτ product of 1.0×10 -4 cm 2 V -1 , while the F-1D tablet had a larger μτ product of 1.8×10 -4 cm 2 V -1 , which can be explained by the relaxed microstrain and pinhole-free characteristics of the F-1D tablet.Respond speed.The response time of the detector is characterized to evaluate the detector response speed, and response time of τon of 172 μs and τoff of 128 μs is derived from the on/off response of an oscilloscope for the detector.The gain factor (G) can be described by:

Supplementary
where τ is the charge carrier lifetime, which determines the device response time.t is the charge carrier transit time, which can be calculated by: Therefore, a large charge carrier mobility and electric field product can result in a small transit time and a large device gain, consistent with the 1D In our imaging system, to conveniently connect the electrode arrays on the X-ray imager with the computer, we design a probe card as the signal readout terminal, as shown in Supplementary Then the solution was filtered in a 20 mL glass bottle with a 0.22 μm filter immediately.The bottle was sealed and put on a heat plate of 60℃.After ~2 h, the crystals with yellowish-brown or lightyellow color begin to deposit (The specific precipitation color is related to precipitation temperature, solution concentration, and raw material purity, but their XRD spectra are consistent).
Growth of 2D (C10N2H15)2PbI4 crystal. 1) TAI (1.722 g, 6 mmol) and PbI2 (1.383 g, 3 mmol) were dissolved in 3 mL ACN, and sonicated for ~0.5 h under room temperature to make a clear solution.Then the solution was filtered in a 20 mL glass bottle with a 0.22 μm filter immediately.
The solution was sealed in a bottle and put on a heat plate of 70℃.After ~15 minutes, the crystals with organ color begin to deposit; 2) TAI (1.722 g, 6 mmol) and PbI2 (1.383 g, 3 mmol) were dissolved in 3 mL ACN, and sonicated for ~0.5 h under room temperature to make a clear solution.
Then the solution was filtered in a 20 mL glass bottle with a 0.22 μm filter immediately.Add 3 mL EA to the filtered solution in a sealed bottle, then put the solution on a heat plate of 70℃.After ~15 minutes, the crystals begin to deposit; 3) TAI (1.722 g, 6 mmol) and PbI2 (1.383 g, 3 mmol) were dissolved in 3 mL ACN, and sonicated for ~0.5 h under room temperature to make a clear solution.Then the solution was filtered in a 20 mL glass bottle with a 0.22 μm filter immediately, and put in EA bath for ~24 h, the crystals begin to deposit.

Supplementary Figure 1 :
Crystal image of the TA-based perovskite.a, sheet-like 1D TA4Pb3I10 single crystals.b, sheet-like 2D TA2PbI4 single crystal.

Supplementary Figure 3 :
Perovskite dimension transition.a, XRD spectra of 1D single crystal TA4Pb3I10 before and after heat treatment.b, XRD spectra of 1D powder before and after heat treatment.No new peaks appeared in both the single crystal or powder cases.c, XRD spectra of the 1D tablet before and after heat treatment, dimension transition occurred.d, microstrain variation with heating time.

Supplementary Figure 4 :
The Williamson-Hall (W-H) calculation results of the tablets in different conditions.(a-f) represent the as-prepared state, heat-treat for 0.5 h, 1 h, 1.5 h, 4 h, and 8 h, respectively.We conclude the XRD spectra of A-1D, A-2D and T-2D to confirm the structure change during the dimension transition process.The small-angle shift of Peaks of T-2D indicates that organic part TA + arranged as a more loosely packed mode than A-2D.

Supplementary Figure 7 :
The Williamson-Hall (W-H) calculation.The Williamson-Hall (W-H) calculation results of the TA-based perovskite tablets in different conditions.The slopes of the fitting lines in (a-g) represent the microstrain in various states. 0

Supplementary Figure 9 :
Energy band structures of TA-based perovskites.a, the ultravioletvisible absorption spectra of 1D and 2D perovskite.b-c, the UPS measurements.d-e, the energy band diagrams of the 1D and 2D perovskite.

e
Supplementary Figure 11: Solid-state 2D 13 C{ 1 H} NMR spectrum.Solid-state 2D 13 C{ 1 H} NMR spectrum acquired from bulk TA-based perovskite with a 1D 13 C CP MAS NMR spectrum along the top horizontal axis and a single-pulse 1 H MAS spectrum along the left vertical axis.Star identifier (*) in Supplementary Figure 11 refers to the rotating sideband.IR measurements of the reversible dimension transition process.only N-H bonds at 3375 cm - 1 show up.After thermal annealing, the infrared vibration peak of H-N-H bonds at 3375 cm -1 merges, representing a more loosely packed mode in the T-2D case.And as we can see, after reversibly water treatment, the infrared vibration peak of H-N-H disappears again, indicating the recovery of the closely packing mode in the A-1D case.

Supplementary Figure 17 :
Sensitivity fitting lines of the tablets after various soaking hours in water.
Long-term water stability of the 2D tablet.a, image of the asprepared 2D tablet.b-c, images of the 2D tablet after soaking into the water for 0 and 1 minute.de, images of the 2D tablet after soaking into the water for 31 and 48 days.
And when the operating temperature was up to 150℃, an unstable baseline occurred in the A-1D case, while the F-1D remained stable.The F-1D tablets are more thermally stable.Supplementary Figure20: Temperature-dependent X-ray response characterization.On-off response of A-1D tablet (a) and F-1D table (b) to hard X-ray with tube voltage of 120 kVp.

Figure 21 :
Temperature-dependent X-ray response sensitivity.Sensitivity fitting of the A-1D (a) and F-1D tablets (b) under various operating temperatures.